Paclitaxel-loaded expansile nanoparticles enhance chemotherapeutic drug delivery in mesothelioma 3-dimensional multicellular spheroids

Our plain-English summary of Paclitaxel-loaded expansile nanoparticles enhance chemotherapeutic drug delivery in mesothelioma 3-dimensional multicellular spheroids, by H. Lei, S.C. Hofferberth, R. Liu, et al (The Journal of Thoracic and Cardiovascular Surgery, 2015).

The study

• Authors: H. Lei, S.C. Hofferberth, R. Liu, A. Colby, K.M. Tevis, P. Catalano, M.W. Grinstaff, Y.L. Colson
• Journal: The Journal of Thoracic and Cardiovascular Surgery
• Published: 2015;149(5):1417-24; discussion 1424-25.e1
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: Intraperitoneal administration of paclitaxel-loaded expansile nanoparticles (Pax-eNPs) significantly improves survival in an in vivo model of malignant mesothelioma compared with conventional drug delivery with the clinically utilized Cremophor EL/ethanol (C/E) excipient. However, in vitro monolayer cell culture experiments do not replicate this superior efficacy, suggesting Pax-eNPs utilize a unique mechanism of drug delivery. Using a mesothelioma spheroid model, we characterized the mechanisms of enhanced tumor cytotoxicity leveraged by Pax-eNPs.

Methods: Human malignant mesothelioma (MSTO-211H) spheroids were co-incubated for 24 hours with Oregon Green-conjugated paclitaxel dissolved in C/E or loaded into eNPs. Oregon Green-paclitaxel uptake was measured as Oregon Green intensity via confocal microscopy and kinetics of tumor cytotoxicity were assessed via propidium iodide staining. Pharmacologic endocytotic inhibitors were used to elucidate mechanisms of eNP uptake into spheroids.

Results: Increased drug penetration and a 38-fold higher intraspheroidal drug concentration were observed 24 hours after MSTO-211H spheroids were treated with Oregon Green-conjugated paclitaxel loaded into eNPs compared with Oregon Green-conjugated paclitaxel dissolved in C/E (P < .01). Macropinocytosis was the dominant endocytotic pathway of eNP uptake. Spheroids were more susceptible to paclitaxel when delivered via eNP, exhibiting more than twice the propidium iodine intensity compared with an equivalent paclitaxel-C/E dose.

Conclusions: Compared with monolayer cell culture, the in vitro 3-D tumor spheroid model better reflects the superior in vivo efficacy of Pax-eNPs. Persistent tumor penetration and prolonged intratumoral release are unique mechanisms of Pax-eNP cytotoxicity. 3-D spheroid models are valuable tools for investigating cytotoxic mechanisms and nanoparticle-tumor interactions, particularly given the costs and limitations of in vivo animal studies.

Copyright © 2015 The American Association for Thoracic Surgery. Published by Elsevier Inc. All rights reserved.

In plain English

This was a laboratory study of cells grown in dishes. It did not involve people, animals or asbestos exposure. The authors grew a human malignant mesothelioma cell line (MSTO-211H) into small three-dimensional cell clusters called spheroids. They compared two ways of delivering the cancer drug paclitaxel: loaded into expansile nanoparticles, or dissolved in the standard Cremophor EL/ethanol solution. After 24 hours, spheroids treated with nanoparticles held 38-fold more labeled paclitaxel than spheroids given the same dose in the standard solution. Seventy-two hours after the drug was washed out, the nanoparticle-treated spheroids still held more than 3 times the standard solution's peak level. Nanoparticle uptake was consistent with macropinocytosis, a way cells engulf material. Markers of cell death rose over the days after nanoparticle treatment. After a 4-hour high-dose treatment, a stain marking dead (necrotic) cells was more than twice as strong with nanoparticles as with the standard solution at 72 hours. The authors concluded that the spheroid model better reflects the nanoparticles' greater effect seen in living animals than flat cell cultures do. They noted that their model lacks the multiple cell types found in real tumors.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory (in vitro) experiment using three-dimensional multicellular tumor spheroids grown from a human mesothelioma cell line
• Who was studied: Spheroids made from the human malignant mesothelioma cell line MSTO-211H, studied at Brigham and Women's Hospital and Boston University. Experiments were repeated at least 3 times with 4 to 8 spheroids per condition. No human subjects or asbestos-exposed people were studied.
• Exposure: Not asbestos. Spheroids were treated with the chemotherapy drug paclitaxel, either loaded into expansile nanoparticles (Pax-eNPs) or dissolved in Cremophor EL/ethanol (Pax-C/E). The main dose was 100 ng/mL paclitaxel for 24 hours; a second experiment used 1000 ng/mL for 4 hours. Some experiments used fluorescently labeled paclitaxel or labeled nanoparticles.
• Main results:
  • After 24 hours, spheroids treated with nanoparticle-delivered labeled paclitaxel showed 38-fold greater drug delivery than spheroids given an equivalent dose in Cremophor EL/ethanol (8.85 x 10^5 vs 0.23 x 10^5 arbitrary units; P less than .0001).
  • Even after a 72-hour washout, labeled-paclitaxel intensity in nanoparticle-treated spheroids was more than 3 times the peak intensity reached with the Cremophor EL/ethanol formulation without washout.
  • Nanoparticle uptake into spheroids increased with dose: there was 8.5 times greater uptake at the higher of two nanoparticle concentrations tested.
  • Pretreatment with wortmannin, and with sodium azide plus 2-deoxyglucose, reduced nanoparticle uptake by 89.8% (plus or minus 2.5%) and 77.4% (plus or minus 13.3%) respectively. The authors stated that this is consistent with the macropinocytosis pathway.
  • In spheroids treated with paclitaxel-loaded nanoparticles, caspase-3 activity (a sign of apoptosis, a form of programmed cell death) was negligible in the first 24 hours. At 48 and 72 hours it was 17-fold and 30-fold higher than at 24 hours.
  • After a 24-hour exposure at 100 ng/mL, the necrosis stain (propidium iodide) was similar for both formulations through 72 hours after washout. Over 7 days it continued to increase in nanoparticle-treated spheroids and decreased in Cremophor EL/ethanol-treated spheroids (P = .0009).
  • After a 4-hour exposure at 1000 ng/mL, propidium iodide intensity at 72 hours after washout was more than twice as high with nanoparticles as with Cremophor EL/ethanol (8.2 x 10^5 vs 3.9 x 10^5 arbitrary units; P = .0030).
• The authors' conclusion: The authors concluded that, compared with standard monolayer cell culture, the 3-D mesothelioma spheroid model better reflects the increased tumor-killing effect of paclitaxel-loaded nanoparticles seen in living animals. They stated that their results support the hypothesis that the nanoparticles' superior effect in animals is secondary to early, persistent tumor penetration and prolonged drug release inside the tumor. They also suggested spheroid models may be useful for preclinical screening.
• Limitations the authors state:
  • The 3-D spheroid model makes quantitative assessment difficult without disrupting the spheroid structure.
  • The multiple cell types commonly present within tumors were not included, which limits how well the model replicates the tumor microenvironment.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelioma, Malignant Mesothelioma.

Related studies

• Paclitaxel-loaded expansile nanoparticles in a multimodal treatment model of malignant mesothelioma — M.D. Schulz, K.A. Zubris, et al. (2011)
• Nanoparticle tumor localization, disruption of autophagosomal trafficking, and prolonged drug delivery improve survival in peritoneal mesothelioma — R. Liu, A.H. Colby, et al. (2016)
• Curcumin loaded PLGA-poloxamer blend nanoparticles induce cell cycle arrest in mesothelioma cells — L. Mayol, C. Serri, et al. (2015)
• Into another dimension: Assessing novel therapeutics in a more lifelike microenvironment — M.B. Antonoff (2015)
• Nanoparticle drug-delivery systems for peritoneal cancers: a case study of the design, characterization and development of the expansile nanoparticle — A.H. Colby, N.H. Oberlies, et al. (2017)
• The performance of expansile nanoparticles in a murine model of peritoneal carcinomatosis — Y.L. Colson, R. Liu, et al. (2011)

Browse more research in The Journal of Thoracic and Cardiovascular Surgery, or return to medical research.